My English is not good enough for me to give you an exact translation but here is the gist:
Urine and feces from edible animals (i.e. animals that we are allowed to eat) are considered pure. But if if we have good reasons to think or if we know that these animals have been drinking or eating najasah then urine and feces from these animals are considered najis. If we are unsure, did they eat najasah or not, then the feces and urine from such animals are pure.

Approximately
The remains of permissible foods, in urine or feces or droppings, whatever is not used [in the form of] permissible food is impure.
If it is confirmed or thought that [something] has used it - eaten it or drank it - then its excrement is impure.
But it is not impure if we only suspect it to be so; one has to confirm that it is or think that it is.The section in green is not totally clear to me but I think that's what it means.
Islamic jurists distinguish between تحقيق confirmation , ظن thinking , شك suspecting as exemplified here.

Iskandari
Im quite sure the passage is not about permissible food. The expression "Mubaah al-akl" does not refer to permissible food, but rather to animals that we are allowed to eat. The word fadlah is not refering to remains but rather to urine and feces from animals. This is quite clear when you read what follows "min rawth..." These are different types of feces from different animals. They are all considered pure in the Maliki school unless we know or have good reasons to think that the animals have been eating najasa. In that case the feces and urine will be considered impure.

I havent seen the whole text but im almost 100 % sure that if we could see the rest of the chapter we would come to the a'yaan al-najisah and there it would say that feces and urine from animals that we aren't allowed to eat are najis.

Approximately
The remains of permissible foods, in urine or feces or droppings, whatever is not used [in the form of] permissible food is impure.
If it is confirmed or thought that [something] has used it - eaten it or drank it - then its excrement is impure.
But it is not impure if we only suspect it to be so; one has to confirm that it is or think that it is.The section in green is not totally clear to me but I think that's what it means.
Islamic jurists distinguish between تحقيق confirmation , ظن thinking , شك suspecting as exemplified here.

You're probably right. The excrement of those animals which are permissible to eat. But the rest of the translation I would still keep the same.
Maybe ما لم يستعمل مباح الأكل means 'unless we use the actual animal that it's permissible to eat'?

Yes according to the Malikis bird droppings are pure. This is what is said in the text (unless they eat or drink things that are najis). But according to others, the Shafi'is for example, they are considered impure.

You're probably right. The excrement of those animals which are permissible to eat. But the rest of the translation I would still keep the same.
Maybe ما لم يستعمل مباح الأكل means 'unless we use the actual animal that it's permissible to eat'?

Click to expand...

I think the confusion comes from how you read this. I believe مباحُ الأكل is a فاعل here, and the verb is يَسْتعمِل in the active voice not the passive.